PRIOR ARTS
As for a grab bucket for loading and unloading the scrapped materials, there have been disclosed some kinds of grab buckets such as a lifting magnet type or claw opening and closing type.
The disc type electromagnet suspended by a crane is excited to attract the scrap. After loading the scrap by the operation of said disc type electromagnet, the electromagnet is excited to separate the scrap. In the grab bucket of the claw type, the upper portion of the semicircular type claw is rotatably supported on the main body suspended from the crane and the claws are opened and closed by means of hydraulic cylinders connected to each of the claws, respectively.
However, in the case of the lifting electromagnet type, the scrap is attracted only in the vicinity of the bottom surface of the electromagnet, thus loading efficiency is not very good because the amount of the scrap to be carried out in each operation is limited. If stoppage of electric current should occur during operation, the scrap unexpectedly falls down.
In the case of a claw opening and closing type grab bucket, it is possible to increase the amount of the scrap to be loaded and unloaded in each time of operation but there have been designated the following demerits.
(1) There is a fear that the scrap is spilled during loading or unloading. PA1 (2) As the claw of semicircular type expands sideways during opening operation of the claw, it is not possible to perfectly unload the scrap on the corner of the bed of the truck. PA1 (3) When dredging the scrap on the bed of the truck is required, the claw may damage the bed surface of the truck. It is, therefore, not possible to dredge the scrap satisfactorily. PA1 (4) When grabbing the scrap on the bed of the truck is carried out, the scrap overflowed from between the claws may damage the side boards of the truck.